High-speed photographic silver halide emulsions supersensitized with palladium salts



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UFFER ET AL OGRAPHIC SILVER HALIDE EMULSIONS SUPERSENSITIZED WITHPALLADIUM SALTS Filed Aug. 31, 1948 A REC/PROC/T) CURVE FOR EMULSIONSENS/T/ZED WITH POWS/UM CHIOROAURATE AND v JOB/UM THIOCVANA TE ANDF/N/JHED 7'0 $0MEWHAT BELOW OPTIMUM SPEED B= REC/PROCI TY CURVE FOR SAMEEMULi/ON CONTAIN/N6 PUTASJ/UM CHIOROPALLADATE C= REC/PROC/TY (UKVE FURSODIUM THIOCX4NA7 AND we 1 (mc) Z0 FINISHED 7'0 OPTIMUM SPEED EMULFlU/YJfNS/TIZED WITH POTASSIUM CHZORO/IURATE AND 1; REC/FRONT) cum 5 FOR SAMEEMl/U/flN (OHM/NINE Poms/UM CHLOROPALMDATE ROBERT E.S724UFFER WILLIAM F.SMITH JNVENTORS fid A TTORNEYS Patented May 27, 1952HIGH-SPEED-PHOTOGRAPHIC SILVER HAL- IDE EMULSIONS. SUPERSENSITIZED.WITHPALLADIUM SALTS Robert E. Staufier as William F. Smith, Roch ester, N.,Y,, assignors to Eastman Kodak Company, Rochester, N. Y., a corporationof New Jersey ppli a n us 94.8, SerialNo. 47;.108 15 Claims. (01. 95-7)v This invention relates to high speed photographic silver halideemulsions supersensitized with palladium salts.

It is known that high speed photographic silver halide emulsions can beprepared by incorporating in the emulsions labile sulfur sensitizingbodies or gelatins and/or gold compounds. We havenow. found that suchhigh speed emulsions canbe supersensitized by adding to them a palladiumsalt. Thus, the emulsion can be brought tomaximum sensitivity with thegold compound and then be rendered still more sensitive with thepalladium salt, or the emulsion can be brought to a sensitivity short ofthe maximum sensitivity attainable with the gold compound and then. berendered more sensitive with the palladium salt. In addition, we havefound that the palladium salts act as sensitizers for the low intensityportion of the reciprocity curve of such emulsions sensitized with goldcompounds.

It is, accordingly, an object of our invention to provide newsupersensitized high-speed photographic silver halide emulsions. Afurther object is to provide a process for preparing such emulsions.Other objects will become apparent hereinafter.

In accordance with our invention, we incorporate' in a high-speed silverhalide emulsion which is sensitized'with at least one gold compoundand/or at least one sulfur sensitizer, at

least onepalladium salt. The high-speed silver halide emulsionssensitized with at least one gold compound, can be prepared byincorporating at least one gold compound in a photographic silver halideemulsionat any stage of the preparation ofthe emulsion or, when theemulsion iscomplated, e. g. just'before coating of the emulsion. Thegold compound is advantageously employed in a concentration equal to notmore than 0.015 per cent by moles of the silver halide in the emulsion,and in the case of gelatino-silver-bromide (including the so-calledbromoiodide emulsions ofwliich the majority of the halide is bromide,with a few per cent of iodide), the upper limit is advantageously 0.01per cent by moles. Up to 0.015 percent by moles-of the silver halide inthe emulsion, the-amount of, the gold compound can vary widely, asperceptible effects can be obtained with 0.0003 per cent or less.Advantae sly, the lower limit is about 0.001 per cent by moles of the,silver halide in the emulsion. We havefound that from 0.003 per cent toabout 0.005 per cent by moles is advantageously employed in practice,especially when the gold compound is incorporated in the emulsion duringthe. preparation of the emulsion, i. e. especially when the emulsion isdigested in thepresenceof the gold compound.

The gold compounds can be added to theemlllsions at any stage ofthepreparation of the emulsions, i. e. before or during precipitation ofthe silver halides, before or during the first digestion (ripening) ofthe emulsion, beforeor during the second digestion of the emulsion, orthe gold compounds can beadded to the emulsion J'ust beforecoating theemulsion. The gold compounds are advantageously incorporated in theemulsions in the form of their solutions in a suitable solvent, e. g.water, methyl alcohol, ethyl alcohol, etc.

The gold compounds which we have found are most advantageously employedin preparing .the high speed emulsions are the gold halides, such asauric chloride, or complex gold halides, Such as potassium chloroaurate(KAuCli) and sodium chlorcaurate (NaAuCll). However,. gold compounds,such. as auric sulfate, are practically as useful as the, gold halides.Aurous, as well as auric compounds can be used. Complex. gold salts,such as alkali metal aurous thiosulfates, alkali metal aurous sulfites(e. g. sodium or potassium aurous thiosulfate and sodium or potassiumaurous sulfite), and a complex salt formed by the interaction. ofthiourea and auric chloride, are also suitable. Potassium chloroaurite,potassium bromoaurite, potassium iodoaurite, potassium auricyanide,potassium aurithiocyanate or the corresponding sodium, calcium,strontium, cadmium or gallium salts can alsobe used.Pyridinotrichloro-gold, ethylenediamine-bis-trichlorogold,diethyl-monobromo-gold and diethyl gold acetone and gold complexes withsulfur compounds'such as are commonly present in gelatin, e. g. the goldthiosinamine complexes, canalso be used.

Sulfur sensitizers are advantageously also added to the emulsions.Gelatins normally contain certain sulfur compounds which act assulfursensitizers of" photographic emulsions, but beneficial efiectsa'reobtained in accordance with our invention by adding sulfur sensitizers,i. e. sulfur compounds containing C=S groups or SS- groups, e. g.thiourea, allyl isothiocyanate, thiosinamine (allylthiourea) etc.Beneficial efiects are also obtained byadding metal or ammoniumthiocyanates, e. g.,sodium, potasslum, ammonium, calcium or cadmiumthiocyanates, to the emulsion. of course, .thiocyanates containingcations which cations areknown to h v in themselves, a del teriouseffect on silver halide emulsions should be avoided. Otherwise thebeneficial eiiects of the thiocyanate would be partially nullified bythe deleterious efiect of the cation. Thus, iron thiocyanate should beavoided. One or more sulfur sensitizer can be employed, and one or morethiocyanates selected from the group consisting of metal and ammoniumt-hiocyanates can be employed in conjunction with a sulfur sensitizerother than a thiecyanate containing a cation selected from the groupconsisting of metal and ammonium cations. The sulfur sensitizers areadvantageously incorporated in the emulsions in the form of theirsolutions in a suitable solvent, such as water, methyl or ethyl alcohol.

The sulfur sensitizers can be incorporated in the emulsions at any stageof the preparation of the emulsion, e. g. during the precipitation ofthe silver halides, during the first digestion (ripening) or during thesecond digestion of the emulsion. When incorporating thiocyanates in theemulsions prior to washing the amount can vary widely. Advantageously,however, an

amount of thiocyanate equal to from about 2 to about 15 per cent bymoles of the silver halide in the emulsion is advantageously employed.If the thiocyanate or other sulfur sensitizer is not added until laterin the preparation of the emulsion, e. g. after washing, it isadvantageous to employ an amount equal to from about 0.1 to about 2.5per cent by moles of the silver halide present in the emulsion in thecase of metal and ammonium thiocyanates, and an amount equal to fromabout 0.006 to about 0.06 per cent by moles of the silver halide in thecase of other sulfur sensitizers.

It is advantageous to digest, i. e. heat treat the emulsion with thegold compound with or without the sulfur sensitizer, at an appropriatetemperature, e. g. at from 100 to 150 F. During digestion, i.e. thesecond digestion as contrasted with the first digestion or ripening, thepH of the emulsion is advantageously adjusted to the acid side ofneutrality, e. g. between 5 and 7. Maintenance of the emulsion on theacid side of neutrality during coating of the emulsion is alsoadvantageous.

. The palladium salts which we employ in practicing our invention can berepresented by the following general formulas:

MzPdXs and MzPdX4 wherein M represents a member selected from the groupconsisting of an alkali metal atom and an ammonium radical, and Xrepresents a halogen atom selected from the group consisting ofchlorine, bromine and iodine atoms. Typical of such palladium salts are:ammonium chloropalladate, potassium chloropalladate, sodiumchloropalladate, ammonium chloropalladite, sodium chloropalladite,potassium bromopalladate, potassium iodopalladate, etc.

The palladium salts are advantageously added to the emulsion just beforecoating the emulsion, but can be added at any time to the finishedemulsions. One or more of the palladium salts can be used. The palladiumsalts are advantageously incorporated in the emulsions in the form oftheir solutions in a suitable solvent, e. g. water, methyl alcohol, etc.

The palladium salts are advantageously employed in a concentration offrom 0.015 to 0.2 per cent by moles of the silver halide in theemulsion. Usually from 0.3 to 0.15 per cent by moles produces themaximum supersensitizing effect.

Palladium salt, ercent by moles of Speed silver halide in the emulsion)Gamma Fog 110118 (N H4) 2PdC1c(0.05) (NH4)2Pd 0140.05) KzPdChfllOfi)Example 2 A high speed photographic gelatino-silverbromide emulsion ofthe negative type sensitized with potassium chloroaurate (KAuCh) andsodium thiocyanate was prepared and finished to optimum speed. Potassiumchloropalladate was added to the emulsion. The emulsion was coated on aglass plate, the coated plate dried and then tested in a sensitometer,development being at 68 F. for 5 minutes in Eastman Kodak Companys BK-50developer. Results were as follows:

Potassium Ohloropallate. (percent by moles of silver halide in theemulsion) Gamma The palladium salts act to sensitize the emulsionssensitized with the gold compounds, for the low-intensity portion of thereciprocity curve. For many purposes, such as astronomical andspectroscopic photography, it is useful to have photographic emulsionsshowing a low reciprocity failure at low intensities. The effect of thepalladium salts in this respect is apparent from the curves in theaccompany drawing. Fig. 1 shows reciprocity curves for the emulsion ofExample 1 (with and without KzPdCls) in which log I (meter candles) isplotted against log It (meter candle seconds) (density:l.0+fog) in themanner customarily employed to illustrate reciprocity law failure (seeThe Theory of the Photographic Process, C. E. K. Mees, page 242,MacMillan Company, New York, 1942). Curve A represents the emulsionwithout the palladium salt and curve B represents the emulsion with thepalladium salt. It will he observed that the emulsion containing thepalladium salt shows distinctly lower reciprocity failure at lowintensities than does the emulsion without the palladium salt, curveB'curving upwards only at about 10 seconds, while curve A shows anupward slope at less than second exposure. The ideal, of course, wouldbe a straight-line curve throughout the entire range of exposures.

Fig. 2 shows reciprocity curves for the emul sions of Example 2, (withand without KzPdCls) in which log I is plotted against log It(dentitreingside) :1. Crime (3. in Fig. 2 represents the emulsionwithout the palladium salt and curve D. represents the emulsion withpalladiumisalt. It.:wil1'.be observed that .theemul- .sionj containing,the palladium salt shows distinctly lower reciprocity failure especiallyat the lower intensities.

The emulsions prepared in accordance with Our-invention canhecoatedin-therusual manner on supports such as. glass, photographic film base,e. g. cellulose. acetate type, photographic paper-base, etc. Sensitizing.dyes of: all types can be employed to spectrally sensitize our newemulsions, e. g. erythrosin, .Congo'Red, any of the sensitizing oya-ninedyes, any of the sensitizing merocyanine dyes v(see United States Patent2,078,233, dated April '27, 1937, forexamplez, any of thesensitizing'hemicyaninedyes (see United StatesIPa-tent 2,166;736, dated July 18,1939, for example) and of thesensitizing hemioxonol dyes (see UnitedStates Patent 2,165,339, dated July 11,1939, for example), etc.

Our invention is directed primarily to the customarily employedphotographic silver halide developing-out emulsions, e. g. silverchloride, silver chlorobromide, silver chlorobromoiodide, silver bromideand silver bromoiodide developingout emulsions. A suitablegelatino-silver-halide emulsion is described, for example, by A. P. H.Trivelli and W. F. Smith, Phot. J. 79, 330 (1939). Such an emulsion canbe prepared as follows:

In a container equipped with a temperature control was put a solution ofthe following composition:

A. potassiumv bromide Mug 825 gelatin ,ig 325 Water cc 8,500

and' in another container was put a solution consisting of:

B. silver nitrate g 1,000 water cc 10,000

Solution A was kept at a temperature of 70 C. and solution .B was put ina separator-y funnel at a temperature 015172 C. Solution B was allowedto run, in minutes, from the separatory funnel through a calibratednozzle into solution A which was kept in constant motion during theprecipitation of the silver halide. After precipitation of the silverhalide, the resulting emulsion while being kept in constant motion wasripened for 20 minutes at 70" C. Then, the emulsion was cooled asquickly as possible to C. and at this temperature, 1250 g. of washedgelatin were added to the emulsion. The emulsion was stirred for 20minutes at 45 C. in order to dissolve the gelatin. After standingovernight in a cold storage room (10 C.), the emulsion was shredded andwashed. It was then melted at a temperature of 42 C. Theweight of theemulsion was brought to 31.5 kgs. by adding 500 g. of gelatin soaked inthe required amount of distilled water. The emulsion was then finishedat C. to the desired speed, in the presence of one or more'goldcompounds and one or more sulfur sensitizers (see Examples 1 and 2).

The sensitization of photographic silver halide emulsions by meansofgold compounds-alone, or with sulfur sensitizers is well known inthe-art.

What we claim as" our, invention and desire to be secured by LettersPatent of"the- United States is:

l. A high speed photographic silver halide emulsion sensitized with atleast one gold compound; in. a conoerltrziltionv equalzto 000031111300;015% by males of the silver hElj-dkliilrithfi emulsion, said emulsion.containing. as a supersensitizer, at least one palladium salt. selectedfrom the group consisting of. 'palladium salts represented by thefollowing, general formulas:

wherein M represents a member selected from the group consisting .of analkali metal atomand an ammonium radical, andX represents a. halogenatom selectedfrom the group consis'tingof chlorine, bromine and .iodineatoms, the concentration of said palladium salt in the. emulsion beingequal to from 0.015 to 0.2% by moles of. the silver halide in theemulsion.

2. A high speed photographic gelatino-silverhalide developing-outemulsion sensitized-with. at least .onegold compound in a concentration:equal to from 0.001. to 0.01% by moles of'the-sllyer halide in theemulsion, said emulsion containing as a supersensitizer. .at least onepalladium salt selected from; the group consisting of palladium saltsrepresented by the following general formulas:

MzPdXs and M2PdX4.

wherein M represents a member selected from the group consisting of analkali metal atom and an ammonium radical, and X represents a halogenatom selected from the group consisting of chlorine, bromine and iodineatoms, the concentration of said palladium salt.- in the emulsion beingequal to from 0.015 to 0.2% by moles of'the silver halidein theemulsion.

3. A high speed. photographic gelatino silverhalide. developing-out.emulsion sensitized withat least one gold salt selected from thoserepresented by the following. general formula:

wherein M represents an, alkali metal atom, said emulsion containing;asa supersensitizer; at least one palladium salt selected from thoserepresented by 'the" followinggeneral formula:

M'zPdCle wherein M represents an alkali metal atom, the concentration ofsaid .gold. salt being equal to from 0.001 to0.0l% by moles of thesilverhalide in the emulsion and the concentration. of said palladium saltbeing equal to from 0.015 to 0.2% by moles of the silver halide in theemulsion.

4. A high speed photographic gelatinoesilverhalide developing-outemulsion sensitized with potassium chloroaurate (KAuCl-r) in a.concentration equal to from 0.001 to 0.01% by moles'of the silver halidein the emulsion, said emulsion containing, as a supersensitizer,potassium chloropalladate (KiPdCle) in a concentrationequal to from0.015 to 0.2% by moles of the silver halide in the emulsion.

5. Ahigh speed photographic gelatino-silverhalide developing outemulsion sensitizedv with potassium chloroaurate (KAuCh) in aconcentration equal to from 0.001 to 0.01% by moles of the silver halidein the emulsion, said emulsion containing, as a-supersensitizer,potassium chloropalladite" (K2PC1C14) in a concentration equal to from0.015 to 0.2% by moles of the-silver-halide in the emulsion.

6. A high speed photographic gelatinorsilverhalide developing-outemulsion sensitized with potassium chloroaurate (KAuCh) in.aconcentration equal to from 0'.001.to 0.01% bymoleszof saltsrepresented by the following general formulas MzPdXs and MzPdXa whereinM represents a member selected from the group consisting of an alkalimetal atom and an ammonium radical, and X represents a halogen atomselected from the group consisting of chlorine, bromine and iodineatoms, the concentration of said palladium salt in the emulsion beingequal to from 0.015 to 0.2% by moles of the silver halide in theemulsion.

8. A high speed photographic gelatino-silverhalide developing-outemulsion sensitized with at least one gold compound in a concentrationequal to from 0.001 to 0.01% by moles of the silver halide in theemulsion, and at least one thiocyanate selected from the groupconsisting of alkali metal and ammonium thiocyanates in a concentrationequal to from 0.1 to 2.5% by moles of the silver halide in the emulsion,said emulsion containing, as a superseneitizer, at least one palladiumsalt selected from the group consisting of palladium salts representedby the following general formulas:

MIzPdXs and M2PdX/l wherein M represents a member selected from thegroup consisting of an alkali metal atom and an ammonium radical, and Xrepresents a halogen atom selected from the group consisting ofchlorine, bromine and iodine atoms, the concentration of said palladiumsalt in the emulsion being equal to from 0.015 to 0.2% by moles of thesilver halide in the emulsion.

9. A high speed photographic gelatino-silverhalide developing-outemulsion sensitized with at least one gold salt selected from thoserepresented by the following general formula:

M'AuCh wherein M represents an alkali metal atom, in a concentrationequal to from 0.001 to 0.01% by moles of the silver halide in theemulsion, and at least one thiocyanate selected from the groupconsisting of alkali metal and ammonium thiocyanates in a concentrationequal to from 0.1 to 2.5% by moles of the silver halide in the emulsion,said emulsion containing, as a supersensitizer, at least one palladiumsalt selected from those represented by the following general formula:

MzPdCls wherein M represents an alkali metal atom, the concentration ofsaid palladium salt in the emulsion being equal to from 0.03 to 0.15%

- by moles of the silver halide in the emulsion.

10. A high speed photographic gelatino-silverhalide developing-outemulsion sensitized with potassium chloroaurate (KAuCh) in aconcentration equal to from 0.001 to 0.01% by moles of the silver halidein the emulsion, and at least one thiocyanate selected from the groupconsisting of alkali metal and ammonium thiocyanates in a concentrationequal to from 0.1 to 2.5% by moles of the silver halide in the emulsion,said emulsion containing, as a supersensitizer, potassiumchloropalladate -(K2PdCl6) in a concentration equal to from 0.03 to0.15% by moles of the silver halide in the emulsion.

11. A high speed photographic gelatino-silverhalide developing-outemulsion sensitized with potassium chloroaurate (KAuCh) in aconcentration equal to from 0.001 to 0.01% by moles of the silver halidein the emulsion, and at least one thiocyanate selected from the groupconsisting of alkali metal and ammonium thiocyanates in a concentrationequal to from 0.1 to 2.5% by moles of the silver halide in the emulsion,said emulsion containing, as a supersensitizer, potassiumchloropalladite (KzPdCh) in a concentration equal to from 0.03 to 0.15%by moles of the silver halide in the emulsion.

12. A high speed photographic gelatino-silverhalide developing-outemulsion sensitized with potassium chloroaurate (KAuCh) in aconcentration equal to from 0.001 to 0.01% by moles of the silver halidein the emulsion, and at least one thiocyanate selected from the groupconsisting of alkali metal and ammonium thiocyanates in a concentrationequal to from 0.1 to 2.5% by moles of the silver halide in the emulsion,said emulsion containing, as a supersensitizer, potassium bromopalladate(KzPdBrs) in a concentration equal to from 0.03 to 0.15% by moles of thesilver halide in the emulsion.

13. A process for preparing a high speed photographic silver halideemulsion comprising sensitizing the emulsion with at least one goldcompound in a concentration equal to from 0.0003 to 0.015% by moles ofthe silver halide in the emulsion and adding to the sensitized emulsionat least one palladium salt selected from the group consisting ofpalladium salts represented by the following general formula:

IMzPdXs and M2PdX4 wherein M represents a member selected from the groupconsisting of an alkali metal atom and an ammonium radical, and Xrepresents a halogen atom selected from the group consisting ofchlorine, bromine and iodine atoms, the con centration of said palladiumsalt in the emulsion being equal to from 0.015 to 0.2% by moles of thesilver halide in the emulsion.

14. A process for preparing a high speed photographic silver halideemulsion comprising sensitizing the emulsion with at least one goldcompound in a concentration equal to from 0.001 to 0.01% by moles of thesilver halide in the emulsion and at least one sulfur sensitizer. andadding to the sensitized emulsion at least one palladium salt selectedfrom the group consisting of palladium salts represented by thefollowing general formulas:

MzPdXe and M2PdX4 wherein M represents a member selected from the groupconsisting of an alkali metal atom and an ammonium radical, and Xrepresents a halogen atom selected from the group consisting ofchlorine, bromine and iodine atoms, the concentration of said palladiumsalt in the emulsion being equal to from 0.015 to 0.2% by moles of thesilver halide in the emulsion.

15. A process for preparing a high speed photographic silver halideemulsion comprising sensitizing the emulsion by digesting it on the acidside of neutrality in the presence of at least one gold compound in aconcentration equal to from 0.001 to 0.01% by moles of the silver halidein the emulsion and at least one sulfur sensitizer, and adding to thesensitized emulsion at least one palladium salt selected from the groupconsisting of palladium salts represented by the following generalformulas:

MzPdXs and lVI2PdX4 wherein M represents a member selected from thegroup consisting of an alkali metal atom and an ammonium radical, and Xrepresents a halogen atom selected from the group consisting ofchlorine, bromine and iodine atoms, the con- 10 centration of saidpalladium salt in the emulsion being equal to from 0.015 to 0.2% bymoles of the silver halide in the emulsion.

ROBERT E. STAUFFEER.

5 WILLIAM F. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent: UNITED STATES PATENTS Number Name Date 2,059,642 KankelwitzNov. 3, 1936 2,399,083 Waller et al Apr. 23, 1946 15 2,448,060 Smith eta1 Aug. 31,1948 2,540,086 Baldsiefen et al. Feb. 6, 1951

1. A HIGH SPEED PHOTOGRAPHIC SILVER HALIDE EMULSION SENSITIZED WITH AT LEAST ONE GOLD COMPOUND IN A CONCENTRATION EQUAL TO FROM 0.0003 TO 0.015% BY MOLES OF THE SILVER HALIDE IN THE EMULSION, SAID EMULSION CONTAINING AS A SUPERSENSITIZER, AT LEAST ONE PALLADIUM SALT SELECTED FROM THE GROUP CONSISTING OF PALLADIUM SALTS REPRESENTED BY THE FOLLOWING GENERAL FORMULAS: 